RESUMEN
ABSTRACT: Hereditary angioedema (HAE) is associated with episodic kinin-induced swelling of the skin and mucosal membranes. Most patients with HAE have low plasma C1-inhibitor activity, leading to increased generation of the protease plasma kallikrein (PKa) and excessive release of the nanopeptide bradykinin from high-molecular-weight kininogen (HK). However, disease-causing mutations in at least 10% of patients with HAE appear to involve genes for proteins other than C1-inhibitor. A point mutation in the Kng1 gene encoding HK and low-molecular weight kininogen (LK) was identified recently in a family with HAE. The mutation changes a methionine (Met379) to lysine (Lys379) in both proteins. Met379 is adjacent to the Lys380-Arg381 cleavage site at the N-terminus of the bradykinin peptide. Recombinant wild-type (Met379) and variant (Lys379) versions of HK and LK were expressed in HEK293 cells. PKa-catalyzed kinin release from HK and LK was not affected by the Lys379 substitutions. However, kinin release from HK-Lys379 and LK-Lys379 catalyzed by the fibrinolytic protease plasmin was substantially greater than from wild-type HK-Met379 and LK-Met379. Increased kinin release was evident when fibrinolysis was induced in plasma containing HK-Lys379 or LK-Lys379 compared with plasma containing wild-type HK or LK. Mass spectrometry revealed that the kinin released from wild-type and variant kininogens by PKa is bradykinin. Plasmin also released bradykinin from wild-type kininogens but cleaved HK-Lys379 and LK-Lys379 after Lys379 rather than Lys380, releasing the decapeptide Lys-bradykinin (kallidin). The Met379Lys substitutions make HK and LK better plasmin substrates, reinforcing the relationship between fibrinolysis and kinin generation.
Asunto(s)
Angioedemas Hereditarios , Bradiquinina , Humanos , Lisina , Angioedemas Hereditarios/genética , Fibrinolisina , Metionina , Células HEK293 , Quininógenos , Calicreínas/genética , RacemetioninaRESUMEN
Patients with hereditary angioedema (HAE) experience episodes of bradykinin (BK)-induced swelling of skin and mucosal membranes. The most common cause is reduced plasma activity of C1 inhibitor, the main regulator of the proteases plasma kallikrein (PKa) and factor XIIa (FXIIa). Recently, patients with HAE were described with a Lys311 to glutamic acid substitution in plasminogen (Plg), the zymogen of the protease plasmin (Plm). Adding tissue plasminogen activator to plasma containing Plg-Glu311 vs plasma containing wild-type Plg (Plg-Lys311) results in greater BK generation. Similar results were obtained in plasma lacking prekallikrein or FXII (the zymogens of PKa and FXIIa) and in normal plasma treated with a PKa inhibitor, indicating Plg-Glu311 induces BK generation independently of PKa and FXIIa. Plm-Glu311 cleaves high and low molecular weight kininogens (HK and LK, respectively), releasing BK more efficiently than Plm-Lys311. Based on the plasma concentrations of HK and LK, the latter may be the source of most of the BK generated by Plm-Glu311. The lysine analog ε-aminocaproic acid blocks Plm-catalyzed BK generation. The Glu311 substitution introduces a lysine-binding site into the Plg kringle 3 domain, perhaps altering binding to kininogens. Plg residue 311 is glutamic acid in most mammals. Glu311 in patients with HAE, therefore, represents reversion to the ancestral condition. Substantial BK generation occurs during Plm-Glu311 cleavage of human HK, but not mouse HK. Furthermore, mouse Plm, which has Glu311, did not liberate BK from human kininogens more rapidly than human Plg-Lys311. This indicates Glu311 is pathogenic in the context of human Plm when human kininogens are the substrates.
Asunto(s)
Angioedemas Hereditarios , Angioedemas Hereditarios/genética , Angioedemas Hereditarios/patología , Animales , Bradiquinina/metabolismo , Factor XIIa/metabolismo , Fibrinolisina , Ácido Glutámico , Humanos , Quininógenos/metabolismo , Lisina , Mamíferos/metabolismo , Ratones , Calicreína Plasmática , Plasminógeno/genética , Plasminógeno/metabolismo , Activador de Tejido PlasminógenoRESUMEN
Factor XII (FXII), the zymogen of the protease FXIIa, contributes to pathologic processes such as bradykinin-dependent angioedema and thrombosis through its capacity to convert the homologs prekallikrein and factor XI to the proteases plasma kallikrein and factor XIa. FXII activation and FXIIa activity are enhanced when the protein binds to a surface. Here, we review recent work on the structure and enzymology of FXII with an emphasis on how they relate to pathology. FXII is a homolog of pro-hepatocyte growth factor activator (pro-HGFA). We prepared a panel of FXII molecules in which individual domains were replaced with corresponding pro-HGFA domains and tested them in FXII activation and activity assays. When in fluid phase (not surface bound), FXII and prekallikrein undergo reciprocal activation. The FXII heavy chain restricts reciprocal activation, setting limits on the rate of this process. Pro-HGFA replacements for the FXII fibronectin type 2 or kringle domains markedly accelerate reciprocal activation, indicating disruption of the normal regulatory function of the heavy chain. Surface binding also enhances FXII activation and activity. This effect is lost if the FXII first epidermal growth factor (EGF1) domain is replaced with pro-HGFA EGF1. These results suggest that FXII circulates in blood in a "closed" form that is resistant to activation. Intramolecular interactions involving the fibronectin type 2 and kringle domains maintain the closed form. FXII binding to a surface through the EGF1 domain disrupts these interactions, resulting in an open conformation that facilitates FXII activation. These observations have implications for understanding FXII contributions to diseases such as hereditary angioedema and surface-triggered thrombosis, and for developing treatments for thrombo-inflammatory disorders.
RESUMEN
Prekallikrein (PK) is the precursor of the trypsin-like plasma protease kallikrein (PKa), which cleaves kininogens to release bradykinin and converts the protease precursor factor XII (FXII) to the enzyme FXIIa. PK and FXII undergo reciprocal conversion to their active forms (PKa and FXIIa) by a process that is accelerated by a variety of biological and artificial surfaces. The surface-mediated process is referred to as contact activation. Previously, we showed that FXII expresses a low level of proteolytic activity (independently of FXIIa) that may initiate reciprocal activation with PK. The current study was undertaken to determine whether PK expresses similar activity. Recombinant PK that cannot be converted to PKa was prepared by replacing Arg371 with alanine at the activation cleavage site (PK-R371A, or single-chain PK). Despite being constrained to the single-chain precursor form, PK-R371A cleaves high-molecular-weight kininogen (HK) to release bradykinin with a catalytic efficiency â¼1500-fold lower than that of kallikrein cleavage of HK. In the presence of a surface, PK-R371A converts FXII to FXIIa with a specific activity â¼4 orders of magnitude lower than for PKa cleavage of FXII. These results support the notion that activity intrinsic to PK and FXII can initiate reciprocal activation of FXII and PK in solution or on a surface. The findings are consistent with the hypothesis that the putative zymogens of many trypsin-like proteases are actually active proteases, explaining their capacity to undergo processes such as autoactivation and to initiate enzyme cascades.
Asunto(s)
Coagulación Sanguínea , Bradiquinina/metabolismo , Precalicreína/metabolismo , Sustitución de Aminoácidos , Animales , Factor XII/metabolismo , Células HEK293 , Humanos , Quininógeno de Alto Peso Molecular/metabolismo , Ratones Endogámicos C57BL , Precalicreína/química , Precalicreína/genética , Proteolisis , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismoRESUMEN
The plasma proteins factor XII (FXII) and prekallikrein (PK) undergo reciprocal activation to the proteases FXIIa and kallikrein by a process that is enhanced by surfaces (contact activation) and regulated by the serpin C1 inhibitor. Kallikrein cleaves high-molecular-weight kininogen (HK), releasing the vasoactive peptide bradykinin. Patients with hereditary angioedema (HAE) experience episodes of soft tissue swelling as a consequence of unregulated kallikrein activity or increased prekallikrein activation. Although most HAE cases are caused by reduced plasma C1-inhibitor activity, HAE has been linked to lysine/arginine substitutions for Thr309 in FXII (FXII-Lys/Arg309). Here, we show that FXII-Lys/Arg309 is susceptible to cleavage after residue 309 by coagulation proteases (thrombin and FXIa), resulting in generation of a truncated form of FXII (δFXII). The catalytic efficiency of δFXII activation by kallikrein is 15-fold greater than for full-length FXII. The enhanced rate of reciprocal activation of PK and δFXII in human plasma and in mice appears to overwhelm the normal inhibitory function of C1 inhibitor, leading to increased HK cleavage. In mice given human FXII-Lys/Arg309, induction of thrombin generation by infusion of tissue factor results in enhanced HK cleavage as a consequence of δFXII formation. The effects of δFXII in vitro and in vivo are reproduced when wild-type FXII is bound by an antibody to the FXII heavy chain (HC; 15H8). The results contribute to our understanding of the predisposition of patients carrying FXII-Lys/Arg309 to angioedema after trauma, and reveal a regulatory function for the FXII HC that normally limits PK activation in plasma.
Asunto(s)
Factor XII/química , Factor XIa/química , Angioedema Hereditario Tipo III/sangre , Angioedema Hereditario Tipo III/genética , Angioedemas Hereditarios , Animales , Arginina/química , Coagulación Sanguínea , Bradiquinina/sangre , Catálisis , Proteína Inhibidora del Complemento C1/química , Factor XIIa/química , Células HEK293 , Humanos , Quininógenos/sangre , Lisina/química , Ratones , Ratones Endogámicos C57BL , Calicreína Plasmática/química , Precalicreína/química , Unión Proteica , Proteínas Recombinantes/química , Propiedades de Superficie , Trombina/genéticaRESUMEN
When blood is exposed to variety of artificial surfaces and biologic substances, the plasma proteins factor XII (FXII) and prekallikrein undergo reciprocal proteolytic conversion to the proteases αFXIIa and α-kallikrein by a process called contact activation. These enzymes contribute to host-defense responses including coagulation, inflammation, and fibrinolysis. The initiating event in contact activation is debated. To test the hypothesis that single-chain FXII expresses activity that could initiate contact activation, we prepared human FXII variants lacking the Arg353 cleavage site required for conversion to αFXIIa (FXII-R353A), or lacking the 3 known cleavage sites at Arg334, Arg343, and Arg353 (FXII-T, for "triple" mutant), and compared their properties to wild-type αFXIIa. In the absence of a surface, FXII-R353A and FXII-T activate prekallikrein and cleave the tripeptide S-2302, demonstrating proteolytic activity. The activity is several orders of magnitude weaker than that of αFXIIa. Polyphosphate, an inducer of contact activation, enhances PK activation by FXII-T, and facilitates FXII-T activation of FXII and FXI. In plasma, FXII-T and FXII-R353A, but not FXII lacking the active site serine residue (FXII-S544A), shortened the clotting time of FXII-deficient plasma and enhanced thrombin generation in a surface-dependent manner. The effect was not as strong as for wild-type FXII. Our results support a model for induction of contact activation in which activity intrinsic to single-chain FXII initiates αFXIIa and α-kallikrein formation on a surface. αFXIIa, with support from α-kallikrein, subsequently accelerates contact activation and is responsible for the full procoagulant activity of FXII.
Asunto(s)
Coagulación Sanguínea , Factor XII/metabolismo , Proteolisis , Dominio Catalítico/genética , Factor XIIa/metabolismo , Humanos , Calicreínas/metabolismo , Propiedades de SuperficieRESUMEN
BACKGROUND: During plasma contact activation, factor XII (FXII) binds to surfaces through its heavy chain and undergoes conversion to the protease FXIIa. FXIIa activates prekallikrein and factor XI (FXI). Recently, we showed that the FXII first epidermal growth factor-1 (EGF1) domain is required for normal activity when polyphosphate is used as a surface. OBJECTIVES: The aim of this study was to identify amino acids in the FXII EGF1 domain required for polyphosphate-dependent FXII functions. METHODS: FXII with alanine substitutions for basic residues in the EGF1 domain were expressed in HEK293 fibroblasts. Wild-type FXII (FXII-WT) and FXII containing the EGF1 domain from the related protein Pro-HGFA (FXII-EGF1) were positive and negative controls. Proteins were tested for their capacity to be activated, and to activate prekallikrein and FXI, with or without polyphosphate, and to replace FXII-WT in plasma clotting assays and a mouse thrombosis model. RESULTS: FXII and all FXII variants were activated similarly by kallikrein in the absence of polyphosphate. However, FXII with alanine replacing Lys73, Lys74, and Lys76 (FXII-Ala73,74,76) or Lys76, His78, and Lys81 (FXII-Ala76,78,81) were activated poorly in the presence of polyphosphate. Both have <5% of normal FXII activity in silica-triggered plasma clotting assays and have reduced binding affinity for polyphosphate. Activated FXIIa-Ala73,74,76 displayed profound defects in surface-dependent FXI activation in purified and plasma systems. FXIIa-Ala73,74,76 reconstituted FXII-deficient mice poorly in an arterial thrombosis model. CONCLUSION: FXII Lys73, Lys74, Lys76, and Lys81 form a binding site for polyanionic substances such as polyphosphate that is required for surface-dependent FXII function.
Asunto(s)
Factor XII , Trombosis , Humanos , Animales , Ratones , Factor XII/metabolismo , Precalicreína/metabolismo , Polifosfatos , Células HEK293 , Factor XI/metabolismo , Factor XIIa/metabolismoRESUMEN
Patients with the inherited disorder hereditary angioedema (HAE) suffer from episodes of soft tissue swelling due to excessive bradykinin production. In most cases, dysregulation of the plasma kallikrein-kinin system due to deficiency of plasma C1 inhibitor is the underlying cause. However, at least 10% of HAE patients have normal plasma C1 inhibitor activity levels, indicating their syndrome is the result of other causes. Two mutations in plasma protease zymogens that appear causative for HAE with normal C1 inhibitor activity have been identified in multiple families. Both appear to alter protease activity in a gain-of-function manner. Lysine or arginine substitutions for threonine 309 in factor XII introduces a new protease cleavage site that results in formation of a truncated factor XII protein (Δ-factor XII) that accelerates kallikrein-kinin system activity. A glutamic acid substitution for lysine 311 in the fibrinolytic protein plasminogen creates a consensus binding site for lysine/arginine side chains. The plasmin form of the variant plasminogen cleaves plasma kininogens to release bradykinin directly, bypassing the kallikrein-kinin system. Here we review work on the mechanisms of action of the FXII-Lys/Arg309 and Plasminogen-Glu311 variants, and discuss the clinical implications of these mechanisms.
RESUMEN
Hereditary factor XI (FXI) deficiency is characterized as an autosomal mild to moderate coagulopathy in humans and domestic animals. Coagulation testing revealed FXI deficiency in a core family of Maine Coon cats (MCCs) in the United States. Factor XI-deficient MCCs were homozygous for a guanine to adenine transition resulting in a methionine substitution for the highly conserved valine-516 in the FXI catalytic domain. Immunoblots detected FXI of normal size and quantity in plasmas of MCCs homozygous for V516M. Some FXI-deficient MCCs experienced excessive post-operative/traumatic bleeding. Screening of 263 MCCs in Europe revealed a mutant allele frequency of 0.232 (23.2%). However, V516M was not found among 100 cats of other breeds. Recombinant feline FXI-M516 (fFXI-M516) expressed ~4% of the activity of wild-type fFXI-V516 in plasma clotting assays. Furthermore, fFXIa-M516 cleaved the chromogenic substrate S-2366 with ~4.3-fold lower catalytic efficacy (kcat/Km) than fFXIa-V516, supporting a conformational alteration of the protease active site. The rate of FIX activation by fFXIa-M516 was reduced >3-fold compared with fFXIa-V516. The common missense variant FXI-V516M causes a cross-reactive material positive FXI deficiency in MCCs that is associated with mild-moderate bleeding tendencies. Given the prevalence of the variant in MCCs, genotyping is recommended prior to invasive procedures or breeding.
Asunto(s)
Deficiencia del Factor XI , Animales , Gatos , Factor XI/química , Factor XI/genética , Deficiencia del Factor XI/genética , Deficiencia del Factor XI/veterinaria , Hemorragia/genética , Homocigoto , Mutación MissenseRESUMEN
Circulating platelets exhibit rapid signaling and adhesive responses to collagen that facilitate hemostasis at sites of vessel injury. Because platelets are anuclear, their collagen receptors must be expressed by megakaryocytes, platelet precursors that arise in the collagen-rich environment of the bone marrow. Whether and how megakaryocytes regulate collagen adhesion during their development in the bone marrow are unknown. We find that surface expression of activated, but not wild-type, alpha2 integrins in hematopoietic cells in vivo results in the generation of platelets that lack surface alpha2 receptors. Culture of hematopoietic progenitor cells ex vivo reveals that surface levels of activated, but not wild-type, alpha2 integrin receptors are rapidly down-regulated during cell growth on collagen but reach wild-type levels when cells are grown in the absence of collagen. Progenitor cells that express activated alpha2 integrins are normally distributed in the bone marrow in vivo and exhibit normal migration across a collagen-coated membrane ex vivo. This migration is accompanied by rapid down-regulation of activated surface integrins. These studies identify ligand-dependent removal of activated alpha2 receptors from the cell surface as a mechanism by which integrin function can be negatively regulated in hematopoietic cells during migration between the adhesive environment of the bone marrow and the nonadhesive environment of the circulating blood.
Asunto(s)
Integrina alfa2/metabolismo , Megacariocitos/citología , Trombopoyesis , Animales , Células Sanguíneas/citología , Células de la Médula Ósea/citología , Adhesión Celular , Diferenciación Celular , Línea Celular Tumoral , Movimiento Celular , Colágeno/metabolismo , Colágeno/farmacología , Trasplante de Células Madre Hematopoyéticas , Células Madre Hematopoyéticas/citología , Células Madre Hematopoyéticas/metabolismo , Integrina alfa2/genética , Integrina beta1/metabolismo , Leucemia Basofílica Aguda/patología , Hígado/citología , Hígado/embriología , Megacariocitos/fisiología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Glicoproteínas de Membrana Plaquetaria/deficiencia , Glicoproteínas de Membrana Plaquetaria/genética , Mutación Puntual , Unión Proteica , Quimera por Radiación , Ratas , Proteínas Recombinantes de Fusión/fisiologíaRESUMEN
Thrombin and fibrillar collagen are potent activators of platelets at sites of vascular injury. Both agonists cause platelet shape change, granule secretion, and aggregation to form the primary hemostatic plug. Human platelets express two thrombin receptors, protease-activated receptors 1 and 4 (PAR1 and PAR4) and two collagen receptors, the alpha(2)beta(1) integrin (alpha(2)beta(1)) and the glycoprotein VI (GPVI)/FcRgamma chain complex. Although these receptors and their signaling mechanisms have been intensely studied, it is not known whether and how these receptors cooperate in the hemostatic function of platelets. This study examined cooperation between the thrombin and collagen receptors in platelet adhesion by utilizing a collagen-related peptide (alpha2-CRP) containing the alpha(2)beta(1)-specific binding motif, GFOGER, in conjunction with PAR-activating peptides. We demonstrate that platelet adhesion to alpha2-CRP is substantially enhanced by suboptimal PAR activation (agonist concentrations that do not stimulate platelet aggregation) using the PAR4 agonist peptide and thrombin. The enhanced adhesion induced by suboptimal PAR4 activation was alpha(2)beta(1)-dependent and GPVI/FcRgamma-independent as revealed in experiments with alpha(2)beta(1)- or FcRgamma-deficient mouse platelets. We further show that suboptimal activation of other platelet G(q)-linked G protein-coupled receptors (GPCRs) produces enhanced platelet adhesion to alpha2-CRP. The enhanced alpha(2)beta(1)-mediated platelet adhesion is controlled by phospholipase C (PLC), but is not dependent on granule secretion, activation of alpha(IIb)beta(3) integrin, or on phosphoinositol-3 kinase (PI3K) activity. In conclusion, we demonstrate a platelet priming mechanism initiated by suboptimal activation of PAR4 or other platelet G(q)-linked GPCRs through a PLC-dependent signaling cascade that promotes enhanced alpha(2)beta(1) binding to collagens containing GFOGER sites.
Asunto(s)
Plaquetas/metabolismo , Colágeno/metabolismo , Integrina alfa2beta1/metabolismo , Adhesividad Plaquetaria/fisiología , Receptor PAR-1/metabolismo , Receptores de Trombina/metabolismo , Secuencias de Aminoácidos , Animales , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , Subunidades alfa de la Proteína de Unión al GTP Gi-Go/metabolismo , Humanos , Ratones , Ratones Endogámicos C57BL , Péptidos/genética , Péptidos/metabolismo , Agregación Plaquetaria , Glicoproteínas de Membrana Plaquetaria/metabolismo , Ratas , Receptores de Colágeno/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Receptores de IgG/genética , Receptores de IgG/metabolismo , Transducción de Señal/fisiología , Trombina/metabolismo , Fosfolipasas de Tipo C/metabolismoRESUMEN
Factor XI (FXI) is the zymogen of a plasma protease (FXIa) that contributes to hemostasis by activating factor IX (FIX). In the original cascade model of coagulation, FXI is converted to FXIa by factor XIIa (FXIIa), a component, along with prekallikrein and high-molecular-weight kininogen (HK), of the plasma kallikrein-kinin system (KKS). More recent coagulation models emphasize thrombin as a FXI activator, bypassing the need for FXIIa and the KKS. We took an evolutionary approach to better understand the relationship of FXI to the KKS and thrombin generation. BLAST searches were conducted for FXI, FXII, prekallikrein, and HK using genomes for multiple vertebrate species. The analysis shows the KKS appeared in lobe-finned fish, the ancestors of all land vertebrates. FXI arose later from a duplication of the prekallikrein gene early in mammalian evolution. Features of FXI that facilitate efficient FIX activation are present in all living mammals, including primitive egg-laying monotremes, and may represent enhancement of FIX-activating activity inherent in prekallikrein. FXI activation by thrombin is a more recent acquisition, appearing in placental mammals. These findings suggest FXI activation by FXIIa may be more important to hemostasis in primitive mammals than in placental mammals. FXI activation by thrombin places FXI partially under control of the vitamin K-dependent coagulation mechanism, reducing the importance of the KKS in blood coagulation. This would explain why humans with FXI deficiency have a bleeding abnormality, whereas those lacking components of the KKS do not.
Asunto(s)
Deficiencia del Factor XI , Factor XI , Animales , Factor XI/genética , Factor XI/metabolismo , Deficiencia del Factor XI/genética , Factor XIIa/metabolismo , Femenino , Humanos , Sistema Calicreína-Quinina , Embarazo , Precalicreína/genética , Precalicreína/metabolismoRESUMEN
Factor XI (FXI) is the zymogen of a plasma protease, factor XIa (FXIa), that contributes to thrombin generation during blood coagulation by proteolytic activation of several coagulation factors, most notably factor IX (FIX). FXI is a homolog of prekallikrein (PK), a component of the plasma kallikrein-kinin system. While sharing structural and functional features with PK, FXI has undergone adaptive changes that allow it to contribute to blood coagulation. Here we review current understanding of the biology and enzymology of FXI, with an emphasis on structural features of the protein as they relate to protease function.
Asunto(s)
Factor XI/genética , Factor XI/metabolismo , Humanos , Procesamiento Proteico-PostraduccionalRESUMEN
The plasma zymogens factor XI (fXI) and prekallikrein (PK) are activated by factor XIIa (fXIIa) during contact activation. Polyanions such as DNA and RNA may contribute to thrombosis and inflammation partly by enhancing PK and fXI activation. We examined PK and fXI activation in the presence of nucleic acids, and determine the effects of the cofactor high molecular weight kininogen (HK) on the reactions. In the absence of HK, DNA and RNA induced fXI autoactivation. Proteases known to activate fXI (fXIIa and thrombin) did not enhance this process appreciably. Nucleic acids had little effect on PK activation by fXIIa in the absence of HK. HK had significant but opposite effects on PK and fXI activation. HK enhanced fXIIa activation of PK in the presence of nucleic acids, but blocked fXI autoactivation. Thrombin and fXIIa could overcome the HK inhibitory effect on autoactivation, indicating these proteases are necessary for nucleic acid-induced fXI activation in an HK-rich environment such as plasma. In contrast to PK, which requires HK for optimal activation, fXI activation in the presence of nucleic acids depends on anion binding sites on the fXI molecule. The corresponding sites on PK are not necessary for PK activation. Our results indicate that HK functions as a cofactor for PK activation in the presence of nucleic acids in a manner consistent with classic models of contact activation. However, HK has, on balance, an inhibitory effect on nucleic acid-supported fXI activation and may function as a negative regulator of fXI activation.
Asunto(s)
Coagulación Sanguínea , ADN/metabolismo , Factor XIa/metabolismo , Quininógeno de Alto Peso Molecular/metabolismo , Precalicreína/metabolismo , ARN/metabolismo , Activación Enzimática , Factor XIIa/metabolismo , Humanos , Trombina/metabolismo , Factores de TiempoRESUMEN
Alzheimer's disease (AD) is characterized by neuronal death, neurofibrillary tangles, and senile plaques. Amyloid-beta (Aß) is the major component of plaques and consists of two prominent isoforms, Aß40 and Aß42. As many risk factors for AD are vascular in origin and blood vessel defects in clearing Aß from the brain are a potential key component of AD pathology, we have focused on the neuron-blood vessel interface, and in particular, the vascular basement membrane, which coats blood vessels and physically separates them from neurons. A prominent component of the vascular basement membrane is the extracellular matrix proteoglycan perlecan. Domain V (DV) is the C-terminal domain and is generated by perlecan proteolysis. DV interacts with the α2 integrin and Aß is a ligand for both α2ß1 and αvß1. Due to the known interaction of DV with α2ß1 and α2ß1's requirement for Aß deposition and neurotoxicity, we hypothesized that DV and/or its C-terminal domain, LG3, might alter neurotoxic signaling pathways by directly blocking or otherwise interfering with α2ß1 binding by Aß. Our study suggests that α2ß1 mediates Aß-induced activation of c-Jun and caspase-3, key components of the neurotoxic pathway, in primary cortical and hippocampal neurons. We further demonstrate that DV and/or LG3 may therapeutically modulate these α2ß1 mediated neurotoxic effects suggesting that they or other α2ß1 integrin modulators could represent a novel approach to treat AD. Finally, our results suggest different neurotoxicity susceptibilities between cortical and hippocampal neurons to Aß40 and Aß42 as further underscored by differing neuroprotective potencies of LG3 in each cell type.
Asunto(s)
Péptidos beta-Amiloides/antagonistas & inhibidores , Péptidos beta-Amiloides/metabolismo , Proteoglicanos de Heparán Sulfato/metabolismo , Integrina alfa2beta1/antagonistas & inhibidores , Integrina alfa2beta1/metabolismo , Neuronas/metabolismo , Enfermedad de Alzheimer/metabolismo , Enfermedad de Alzheimer/patología , Animales , Supervivencia Celular/fisiología , Células Cultivadas , Corteza Cerebral/metabolismo , Corteza Cerebral/patología , Femenino , Hipocampo/metabolismo , Hipocampo/patología , Ratones , Ratones Endogámicos C57BL , Neuronas/patología , Embarazo , Transducción de Señal/fisiologíaRESUMEN
Studies with animal models implicate the plasma proteases factor XIIa (FXIIa) and α-kallikrein in arterial and venous thrombosis. As congenital deficiencies of factor XII (FXII) or prekallikrein (PK), the zymogens of FXIIa and α-kallikrein respectively, do not cause bleeding disorders, inhibition of these enzymes may have therapeutic benefit without compromising hemostasis. The relative contributions of FXIIa and α-kallikrein to thrombosis in animal models are not clear. We compared mice lacking FXII or PK to wild type mice in established models of arterial thrombosis. Wild type mice developed carotid artery occlusion when the vessel was exposed to a 3.5% solution of ferric chloride (FeCl3). FXII-deficient mice were resistant to occlusion at 5% FeCl3 and partially resistant at 10% FeCl3. PK-deficient mice were resistant at 3.5% FeCl3 and partially resistant at 5% FeCl3. Mice lacking high molecular weight kininogen, a cofactor for PK activation and activity, were also partially resistant to thrombosis at 5% FeCl3. Induction of carotid artery thrombosis with Rose Bengal was delayed in FXII-deficient mice compared to wild type or PK-deficient animals. In human plasma supplemented with silica, DNA or collagen to induce contact activation, an antibody to the FXIIa active site was more effective at preventing thrombin generation than an antibody to the α-kallikrein active site. Similarly, the FXIIa antibody was more effective at reducing fibrin formation in human blood flowing through collagen coated-tubes. The findings suggest that inhibitors of FXIIa will have more potent anti-thrombotic effects than inhibitors of α-kallikrein.
Asunto(s)
Trastornos de la Coagulación Sanguínea/complicaciones , Deficiencia del Factor XII/complicaciones , Factor XII/genética , Precalicreína/deficiencia , Precalicreína/genética , Trombosis/etiología , Trombosis/genética , Animales , Coagulación Sanguínea/efectos de los fármacos , Trastornos de la Coagulación Sanguínea/genética , Factor XII/antagonistas & inhibidores , Deficiencia del Factor XII/genética , Eliminación de Gen , Humanos , Calicreínas/antagonistas & inhibidores , Calicreínas/genética , Ratones , Ratones Endogámicos C57BL , Precalicreína/antagonistas & inhibidores , Factores Protectores , Trombosis/prevención & controlRESUMEN
OBJECTIVE: Platelets express the α2ß1 integrin and the glycoprotein VI (GPVI)/FcRγ complex, both collagen receptors. Understanding platelet-collagen receptor function has been enhanced through use of genetically modified mouse models. Previous studies of GPVI/FcRγ-mediated collagen-induced platelet activation were perfomed with mice in which the FcRγ subunit was genetically deleted (FcRγ-/-) or the complex was depleted. The development of α2ß1-/- and GPVI-/- mice permits side-by-side comparison to address contributions of these collagen receptors in vivo and in vitro. APPROACH AND RESULTS: To understand the different roles played by the α2ß1 integrin, the GPVI receptor or FcRγ subunit in collagen-stimulated hemostasis and thrombosis, we compared α2ß1-/-, FcRγ-/-, and GPVI-/- mice in models of endothelial injury and intravascular thrombosis in vivo and their platelets in collagen-stimulated activation in vitro. We demonstrate that both the α2ß1 integrin and the GPVI receptor, but not the FcRγ subunit influence carotid artery occlusion in vivo. In contrast, the GPVI receptor and the FcRγ chain, but not the α2ß1 integrin, play similar roles in intravascular thrombosis in response to soluble Type I collagen. FcRγ-/- platelets showed less attenuation of tyrosine phosphorylation of several proteins including RhoGDI when compared to GPVI-/- and wild type platelets. The difference between FcRγ-/- and GPVI-/- platelet phosphotyrosine levels correlated with the in vivo thrombosis findings. CONCLUSION: Our data demonstrate that genetic deletion of GPVI receptor, FcRγ chain, or the α2ß1 integrin changes the thrombotic potentials of these platelets to collagen dependent on the stimulus mechanism. The data suggest that the FcRγ chain may provide a dominant negative effect through modulating signaling pathways in platelets involving several tyrosine phosphorylated proteins such as RhoGDI. In addition, these findings suggest a more complex signaling network downstream of the platelet collagen receptors than previously appreciated.
Asunto(s)
Plaquetas/metabolismo , Colágeno/farmacología , Integrina alfa2beta1/metabolismo , Glicoproteínas de Membrana Plaquetaria/metabolismo , Receptores de IgG/metabolismo , Trombosis/metabolismo , Animales , Colágeno/efectos adversos , Modelos Animales de Enfermedad , Integrina alfa2beta1/genética , Ratones , Ratones Noqueados , Activación Plaquetaria/efectos de los fármacos , Activación Plaquetaria/genética , Glicoproteínas de Membrana Plaquetaria/genética , Ratas , Receptores de IgG/genética , Trombosis/inducido químicamente , Trombosis/genéticaRESUMEN
PURPOSE: The α2ß1 integrin plays an important but complex role in angiogenesis and vasculopathies. Published GWAS studies established a correlation between genetic polymorphisms of the α2ß1 integrin gene and incidence of diabetic retinopathy. Recent studies indicated that α2-null mice demonstrate superior vascularization in both the wound and diabetic microenvironments. The goal of this study was to determine whether the vasculoprotective effects of α2-integrin deficiency extended to the retina, using the oxygen-induced retinopathy (OIR) model for retinopathy of prematurity (ROP). METHODS: In the OIR model, wild-type (WT) and α2-null mice were exposed to 75% oxygen for 5 days (postnatal day [P] 7 to P12) and subsequently returned to room air for 6 days (P12-P18). Retinas were collected at postnatal day 7, day 13, and day 18 and examined via hematoxylin and eosin and Lectin staining. Retinas were analyzed for retinal vascular area, neovascularization, VEGF expression, and Müller cell activation. Primary Müller cell cultures from WT and α2-null mice were isolated and analyzed for hypoxia-induced VEGF-A expression. RESULTS: In the retina, the α2ß1 integrin was minimally expressed in endothelial cells and strongly expressed in activated Müller cells. Isolated α2-null primary Müller cells demonstrated decreased hypoxia-induced VEGF-A expression. In the OIR model, α2-null mice displayed reduced hyperoxia-induced vaso-attenuation, reduced pathological retinal neovascularization, and decreased VEGF expression as compared to WT counterparts. CONCLUSIONS: Our data suggest that the α2ß1 integrin contributes to the pathogenesis of retinopathy. We describe a newly identified role for α2ß1 integrin in mediating hypoxia-induced Müller cell VEGF-A production.
Asunto(s)
Células Ependimogliales/metabolismo , Integrina alfa2beta1/genética , ARN/genética , Retinopatía de la Prematuridad/genética , Factor A de Crecimiento Endotelial Vascular/genética , Animales , Animales Recién Nacidos , Células Cultivadas , Modelos Animales de Enfermedad , Endotelio Vascular/metabolismo , Endotelio Vascular/patología , Células Ependimogliales/patología , Regulación de la Expresión Génica , Integrina alfa2beta1/biosíntesis , Integrina alfa2beta1/deficiencia , Ratones , Ratones Endogámicos C57BL , Microscopía Fluorescente , Oxígeno/toxicidad , Reacción en Cadena de la Polimerasa , Retinopatía de la Prematuridad/inducido químicamente , Retinopatía de la Prematuridad/metabolismo , Factor A de Crecimiento Endotelial Vascular/biosíntesisRESUMEN
Amyloid-ß (Aß) peptide is a key component of amyloid plaques, one of the pathological features of Alzheimer's disease. Another feature is pronounced cell loss in the brain leading to an enlargement of the ventricular area and a decrease in brain weight and volume. Aß plaque deposition and neuronal toxicity can be modeled by treating human cortical neuronal cultures with Aß and showing robust Aß deposition and neurotoxicity that is mediated by α2ß1 and αvß1 integrins. The current study expands on these findings by showing that the domain V of perlecan, a known α2 integrin ligand, inhibits Aß neurotoxicity in an α2 integrin-dependent manner. Additionally, Aß binds more efficiently to cells expressing activated α2 integrin. Finally the inhibition of Aß neurotoxicity with domain V is synergistic with inhibitors of αv integrin and ß1 integrin. We propose that domain V and potentially other α2 integrin ligands could be a new therapeutic approach for inhibiting the Aß plaque deposition and neurotoxicity observed in Alzheimer's disease.
Asunto(s)
Péptidos beta-Amiloides/antagonistas & inhibidores , Péptidos beta-Amiloides/toxicidad , Proteoglicanos de Heparán Sulfato/fisiología , Integrina alfa2/metabolismo , Fragmentos de Péptidos/antagonistas & inhibidores , Fragmentos de Péptidos/toxicidad , Animales , Células Cultivadas , Corteza Cerebral/metabolismo , Corteza Cerebral/patología , Humanos , Ligandos , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Unión Proteica/fisiología , Estructura Terciaria de Proteína/fisiologíaRESUMEN
Mast cells play a critical role in innate immunity, allergy, and autoimmune diseases. The receptor/ligand interactions that mediate mast cell activation are poorly defined. The alpha2beta1 integrin, a receptor for collagens, laminins, decorin, E-cadherin, matrix metalloproteinase-1 (MMP-1), endorepellin, and several viruses, has been implicated in normal developmental, inflammatory, and oncogenic processes. We recently reported that alpha2 integrin subunit-deficient mice exhibited markedly diminished neutrophil and IL-6 responses during Listeria monocytogenes- and zymosan-induced peritonitis. Peritoneal mast cells require alpha2beta1 integrin expression for activation in response to pathogens, yet the ligand and molecular mechanisms by which the alpha2beta1 integrin induces activation and cytokine secretion remain unknown. We now report that the alpha2beta1 integrin is a novel receptor for multiple collectins and the C1q complement protein. We demonstrate that the alpha2beta1 integrin provides a costimulatory function required for mast cell activation and cytokine secretion. This finding suggests that the alpha2beta1 integrin is not only important for innate immunity but may serve as a critical target for the regulation of autoimmune/allergic disorders.